Simplify the following expression: $r = \dfrac{a - 10}{6a + 8} - \dfrac{-5a - 13}{6a + 8}$
Explanation: Since the expressions have the same denominator we simply subtract the numerators: $r = \dfrac{a - 10 - (-5a - 13)}{6a + 8}$ Distribute the negative sign: $r = \dfrac{a - 10 + 5a + 13}{6a + 8}$ Combine like terms: $r = \dfrac{6a + 3}{6a + 8}$